1. Field of the Invention
This invention relates to an electrophotographic photosensitive member for forming an image according to the reversal developing system.
2. Related Background Art
As the photoconductive material of electrophotographic photosensitive member, in place of inorganic photoconductive members of the prior art, various organic photoconductive members have been developed in recent years, and particularly the function separation type electrophotographic photosensitive member having a photosensitive layer comprising a charge generation layer and a charge transport layer laminated has been already practically applied.
The charge generation layer is a layer comprising a resin having a photoconductive pigment dispersed therein, and, for example, those containing a photoconductive material such as azo pigment, perylene pigment, phthalocyanine pigment, squarilium type pigment, etc. dispersed in a resin such as styrene resin, styrene-butadiene copolymer, polycarbonate resin, vinyl butyral resin, etc. have been known.
When an image is formed according to the reversal developing system by use of an electrophotographic photosensitive member having such a charge generation layer having a photoconductive pigment dispersed in the resin and a charge transport layer laminated, ground fog is liable to be generated on the white tone image, and image defect such as black dot will be increased, when successive copying is conducted repeatedly.
Such image defect is not a problem in the positive developing system but a phenomenon particularly conspicuous in the reversal developing system.
For example, when an electrophotographic photosensitive member using a charge transport layer having a perylene pigment dispersed in a butyral resin is employed in the reversal developing system, black dots are outstanding on white tone image.
When an electrophotographic photosensitive member using a charge generation layer having a disazo pigment dispersed in a polycarbonate resin is employed in the reversal developing system, ground fog is generated on white tone image, and density lowering will be generated due to increase of residual potential when successive copying is conducted repeatedly.
On the other hand, when an electrophotographic photosensitive member using a charge generation layer having a phthalocyanine pigment dispersed in an epoxy resin is employed in the reversal developing system, ground fog is generated on white tone image, and black dots are increased when successive copying is conducted repeatedly.
Thus, in the case of forming an image according to the reversal developing system, no electro-photographic photosensitive member excellent in repetition stability in electrophotographic characteristics in repeated use has been found yet under the present situation.